# CVE-2026-64036: cgroup/rstat: validate cpu before css_rstat_cpu() access

> A missing CPU validation in the Linux kernel's cgroup rstat BPF kfunc allows out-of-bounds access, potentially causing a system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-92721, BELL-CVE-2026-64036, DEBIAN-CVE-2026-64036, GHSA-7cqc-fvgj-qm9h, ROOT-OS-DEBIAN-12-CVE-2026-64036, ROOT-OS-DEBIAN-13-CVE-2026-64036, UBUNTU-CVE-2026-64036

## What is CVE-2026-64036?

CVE-2026-64036 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

cgroup/rstat: validate cpu before css_rstat_cpu() access

css_rstat_updated() is exposed as a BPF kfunc and accepts a
caller-provided cpu argument. The function uses cpu for per-cpu rstat
lookups without checking whether it refers to a valid possible CPU.

A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an
invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu ==
0x7fffffff triggers:

  UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9
  index 2147483647 is out of range for type 'long unsigned int [64]'
  Call Trace:
    css_rstat_updated
    bpf_iter_run_prog
    cgroup_iter_seq_show
    bpf_seq_read

Add cpu validation to the BPF-facing css_rstat_updated() kfunc and
move the common implementation to __css_rstat_updated() for in-kernel
callers.

Weakness: CWE-129 (Improper Validation of Array Index), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-64036?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64036?

Apply the vendor's patch.

## Is CVE-2026-64036 being exploited?

There is no known exploitation of CVE-2026-64036 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64036 and fix it if it is affected.

What it is: CVE-2026-64036 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64036 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64036/ (Markdown: https://insights.sbomify.com/CVE-2026-64036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64036
- OSV: https://osv.dev/vulnerability/CVE-2026-64036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64036/
Summaries are generated and may contain mistakes; the official description above is the record.